Air intake and exhaust systems for a snowmobile engine

ABSTRACT

A snowmobile has a frame including a tunnel having a passage therethrough, at least one ski, an engine having an engine air inlet and an engine exhaust outlet, and a drive track operatively connected thereto and disposed at least partly below the tunnel around a rear suspension. A heat exchanger connected to the tunnel has heat exchanger engine air inlet and outlet, a cooling air inlet and a cooling air outlet fluidly connected between the cooling air inlet and the passage. A snowmobile has a pipe fluidly connected to the exhaust outlet and having first and second pipe outlets. The snowmobile further has a muffler having first and second muffler inlets and a muffler outlet, a turbocharger, first and second exhaust flow passages, and a valve disposed between the pipe and the first muffler inlet for selectively controlling the flow of exhaust gas flowing through the first exhaust flow path.

CROSS-REFERENCE

The present application claims priority from U.S. Provisional PatentApplication No. 62/530,553, entitled “Air Intake and Exhaust Systems fora Snowmobile Engine”, filed Jul. 10, 2017, the entirety of which isincorporated herein by reference.

FIELD OF THE TECHNOLOGY

The present technology relates to air intake and exhaust systems for asnowmobile.

BACKGROUND

Design of air intake and exhaust systems are of importance for internalcombustion engines. The efficiency of the combustion process in aninternal combustion engine can be increased by decreasing thetemperature of the air entering the engine for combustion. A decrease inair intake temperature provides a denser intake charge to the engine andallows more air and fuel to be combusted per engine cycle, increasingthe output power of the engine. In addition, the efficiency of thecombustion process can also be increased by compressing the air enteringthe engine for combustion. An increase in air intake pressure alsoprovides a denser intake charge compared to the air from the atmosphereand allows more air and fuel to be combusted per engine cycle, and inturn increasing the output power of the engine. The compression of theair may be of particular importance when the internal combustion engineis operated in environments where atmospheric pressure is low or whenthe air gets thinner, such as when the engine is operated at highaltitudes. The compression of the air can be performed using aturbocharger operated using the flow of exhaust gas of the engine.However, the efficiency and the performance of some engines may behindered under certain circumstances by the presence of a turbochargerbecause of an increased amount of backpressure in their exhaust system.

There is thus a need for air intake systems capable of increasing airdensity before its entry into the engine for the combustion process, andfor exhaust systems for internal combustion engines that are coupled toa turbocharger that could reduce an amount of backpressure under certaincircumstances.

SUMMARY

It is an object of the present technology to ameliorate at least some ofthe inconveniences present in the prior art.

According to one aspect of the present technology, there is provided asnowmobile having a frame including a tunnel. The tunnel has a passagedefined therethrough. The snowmobile further has at least one skiconnected to the frame, an engine supported by the frame and having anengine air inlet, a rear suspension assembly operatively connected tothe tunnel and a drive track supported by the rear suspension assemblyand disposed at least in part below the tunnel. The drive track isoperatively connected to the engine. The snowmobile further includes aheat exchanger connected to the tunnel. The heat exchanger includes aheat exchanger engine air inlet fluidly connected to atmosphere, a heatexchanger engine air outlet fluidly connected between the heat exchangerengine air inlet and the engine air inlet, a cooling air inlet fluidlyconnected to the atmosphere, and a cooling air outlet fluidly connectedbetween the cooling air inlet and the passage of the tunnel.

In some implementations, air flowing from the heat exchanger engine airinlet to the heat exchanger engine air outlet is cooled by air flowingfrom the cooling air inlet to the cooling air outlet.

In some implementations, the air flowing inside the heat exchanger fromthe heat exchanger engine air inlet to the heat exchanger engine airoutlet is fluidly separate from the air flowing inside the heatexchanger from the cooling air inlet to the cooling air outlet.

In some implementations, the snowmobile further includes an intercoolerdisposed inside the heat exchanger. The intercooler defines a first pathfor air flowing from the cooling air inlet to the cooling air outlet,and the intercooler defines a second path for air flowing from the heatexchanger engine air inlet to the heat exchanger engine air outlet. Thefirst path is fluidly separate from the second path, and the first pathis in thermal communication with the second path.

In some implementations, the first path is perpendicular to the secondpath.

In some implementations, the tunnel comprises a left side portion and aright side portion, and the cooling air inlet and the cooling air outletare disposed laterally between the left and right side portions.

In some implementations, the tunnel further includes a top portionconnected between the left and right side portions, and the cooling airinlet and the cooling air outlet are disposed vertically higher than thetop portion.

In some implementations, when the snowmobile is being propelled,rotation of the drive track creates a low pressure zone near thepassage. The low pressure zone induces air to flow into the heatexchanger through the cooling air inlet, exit the heat exchanger throughthe cooling air outlet and to flow through the passage.

In some implementations, the passage is defined in the top portion, aprotrusion is defined rearwardly of the passage on a bottom face of thetop portion, and the low pressure zone is forward of the protrusion.

In some implementations, the heat exchanger is connected to a forwardportion of the tunnel.

In some implementations, the snowmobile further includes a front axleoperatively connected between the engine and the drive track, thepassage being above the front axle and being longitudinally aligned withthe front axle.

In some implementations, the snowmobile further includes an aircompressor fluidly connected between the atmosphere and the heatexchanger engine air inlet to deliver compressed air to the engine viathe heat exchanger.

In some implementations, the air compressor is part of a turbocharger.The engine has an engine exhaust outlet fluidly connected to theturbocharger; and a flow of exhaust gas flows out of the engine throughthe engine exhaust outlet for operating the turbocharger, and then tothe atmosphere via the turbocharger.

In some implementations of the present technology, the heat exchanger isplaced on the top portion of the tunnel of the snowmobile. The heatexchanger is in fluid communication with the passage definedtherethrough. The heat exchanger favours the transfer of heat from thecompressed air coming out of the air compressor to a flow of air fromthe atmosphere flowing from the cooling air inlet to the cooling airoutlet. As such, the heat exchanger cools down the compressed air beforeentering the engine via the engine air inlet. When the drive track ofthe snowmobile rotates below the passage, a zone of low pressure isformed near the passage and the air from the atmosphere is induced toflow through the heat exchanger from the cooling air inlet to thecooling air outlet. Using the rotation of the track for inducing the airfrom the atmosphere to flow through the heat exchanger may reduce thecomplexity of the snowmobile since no additional components, such as afan, are required to induce the flow of the air through the heatexchanger.

According to another aspect of the present technology, there is provideda snowmobile including a frame, at least one ski connected to the frame,an engine supported by the frame. The engine has an engine air inlet andan engine exhaust outlet. The snowmobile further includes a pipe fluidlyconnected to the engine exhaust outlet for receiving a flow of exhaustgas from the engine, and the pipe further includes first and second pipeoutlets. The snowmobile further has a muffler having a first mufflerinlet, a second muffler inlet and a muffler outlet. A first exhaust flowpath is defined from the first pipe outlet to the first muffler inlet,and a second exhaust flow path is defined from the second pipe outlet tothe second muffler inlet. The snowmobile further includes a turbochargerfluidly connected along the second exhaust flow path between the secondpipe outlet and the second muffler inlet, and a valve disposed betweenthe pipe and the first muffler inlet for selectively controlling theflow of exhaust gas flowing through the first exhaust flow path.

In some implementations, the muffler includes first and second expansionchambers. The first muffler inlet is defined in the first expansionchamber. The second muffler inlet is defined in the second expansionchamber. Exhaust gas flowing along the first exhaust flow path flows inthe first expansion chamber, then in the second expansion chamber, andthen through the muffler outlet. The exhaust gas flowing along thesecond exhaust flow path flows in the second expansion chamber and thenthrough the muffler outlet.

In some implementations, the turbocharger includes an air compressorfluidly connected to the engine air inlet; and the snowmobile furtherincludes an air intake system fluidly connecting atmosphere to theengine. The air intake system includes the air compressor, a bypassconduit fluidly connected between the engine air inlet and a portion ofthe air intake system upstream of the air compressor for bypassing theair compressor, and a bypass valve selectively controlling a flow of airflowing in the bypass conduit.

In some implementations, the bypass valve selectively opens below athreshold operating condition of the engine.

In some implementations, the air intake system further includes a heatexchanger fluidly connected downstream from the air compressor forcooling compressed air delivered to the engine air inlet from the aircompressor.

In some implementations, the snowmobile further has an intercoolerdisposed inside the heat exchanger.

In some implementations, the air intake system further includes a firstchamber for receiving air from the atmosphere, and a second chamberfluidly connected between the first chamber and the air compressor.

In some implementations, the valve is a primary valve, and thesnowmobile further includes a primary exhaust conduit fluidly connectingthe first pipe outlet to the first muffler inlet and defining at least aportion of the first exhaust flow path. The primary valve is disposed inthe primary exhaust conduit. The snowmobile further includes a secondaryvalve selectively controlling the flow of exhaust gas flowing throughthe second exhaust flow path.

In some implementations, the snowmobile further has a secondary exhaustconduit fluidly connecting the turbocharger to the second muffler inletand defining at least a portion of the second exhaust flow path, and thesecondary valve is disposed in the secondary exhaust conduit.

In some implementations, the secondary valve is open below a thresholdatmospheric pressure.

In some implementations, the turbocharger has a housing, the valve is aprimary valve, and the snowmobile further includes a primary exhaustconduit fluidly connecting the first pipe outlet to the first mufflerinlet and defining at least a portion of the first exhaust flow path,the primary valve being disposed in the housing of the turbocharger, anda secondary valve selectively controlling the flow of exhaust gasflowing through the second exhaust flow path.

In some implementations, the snowmobile further includes a secondaryexhaust conduit fluidly connecting the turbocharger to the secondmuffler inlet and defining at least a portion of the second exhaust flowpath, and the secondary valve is disposed in the secondary exhaustconduit.

In some implementations, the secondary valve is open below a thresholdatmospheric pressure.

In some implementations, the snowmobile further includes a secondaryexhaust conduit fluidly connecting the turbocharger to the secondmuffler inlet and defining at least a portion of the second exhaust flowpath, and a transfer conduit fluidly connecting the primary andsecondary exhaust conduits. The transfer conduit is positioneddownstream from the primary valve and upstream from the secondary valve.

In some implementations, one of the first and second exhaust flow pathsextends from another one of the first and second exhaust flow paths, andthe valve is an inverted valve that is movable for simultaneouslycontrolling the flow of exhaust gas flowing through the first and secondexhaust flow paths.

In some implementations, the snowmobile further includes a handlebarconnected to the frame. The engine air inlet is forward of thehandlebar.

In implementations of the present technology, the exhaust system has anexhaust pipe that has first and second pipe outlets. The exhaust systemfurther has a muffler having first and second muffler inlets and amuffler outlet. Each pipe outlet defines the beginning of a respectiveexhaust flow path. The first exhaust flow path is defined from the firstpipe outlet to the first muffler inlet, and the second exhaust flow pathis defined from the second pipe outlet to the second muffler inlet. Aturbocharger is fluidly connected along the second exhaust flow pathbetween the second pipe outlet and the second muffler inlet. A valve isdisposed between the pipe and the first muffler inlet for selectivelycontrolling the flow of exhaust gas flowing through the first exhaustflow path.

By controlling the flow of exhaust gas through the first and/or secondexhaust flow path, the engine can be operated as a naturally aspiratedengine under certain circumstances and as a turbocharged engine underother circumstances. The control of the flow of exhaust gas through thefirst and second exhaust flow paths may further assist in reducingbackpressure issues in the exhaust system. Different implementations ofthe exhaust system are contemplated.

According to yet another aspect of the present technology, there isprovided a method for controlling a flow of exhaust gas from an engine.The method involves moving a valve to a first position such that exhaustgas flows sequentially from the engine to a pipe, a first exhaust flowpath, a muffler and atmosphere, and further involves moving the valve toa second position such that exhaust gas flows sequentially from theengine to the pipe, a second exhaust flow path, the muffler and to theatmosphere, a turbine being disposed along the second exhaust flow path.

In some implementations, the valve is moved from the first position tothe second position when the engine is operated above a thresholdoperating condition.

In some implementations, when the valve is in the first position,exhaust gas flowing in the first exhaust flow path has a first amount ofbackpressure, and when the valve is in the second position, exhaust gasflowing in the second exhaust flow path has a second amount ofbackpressure. The second amount of backpressure is less than the firstamount of backpressure.

In some implementations, when the valve is in the first position,exhaust gas flows through a first number of expansion chambers of themuffler, and when the valve is in the second position, exhaust gas flowsthrough a single expansion chamber of the muffler, or a second number ofexpansion chambers of the muffler. The second number is less than thefirst number.

In some implementations, the valve is a primary valve, and the methodfurther includes selectively closing a secondary valve to close thesecond exhaust flow path.

In some implementations, the secondary valve is closed when the engineis operated below a threshold atmospheric pressure.

In some implementations, the method further includes selectively movingthe primary and secondary valves such that exhaust gas flows from thefirst exhaust flow path to the second exhaust flow path.

For purposes of this application, terms related to spatial orientationsuch as forwardly, rearward, upwardly, downwardly, left, and right, areas they would normally be understood by a driver of the snowmobilesitting thereon in a normal riding position. Terms related to spatialorientation when describing or referring to components or sub-assembliesof the snowmobile, separately from the snowmobile, such as a heatexchanger for example, should be understood as they would be understoodwhen these components or sub-assemblies are mounted to the snowmobile,unless specified otherwise in this application.

Implementations of the present technology each have at least one of theabove-mentioned object and/or aspects, but do not necessarily have allof them. It should be understood that some aspects of the presenttechnology that have resulted from attempting to attain theabove-mentioned object may not satisfy this object and/or may satisfyother objects not specifically recited herein. The explanations providedabove regarding the above terms take precedence over explanations ofthese terms that may be found in any one of the documents incorporatedherein by reference.

Additional and/or alternative features, aspects and advantages ofimplementations of the present technology will become apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present technology, as well as otheraspects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingdrawings, where:

FIG. 1 is a left side elevation view of a snowmobile, with a portion ofa drive track represented;

FIG. 2 is a right side elevation view of a portion of the snowmobile ofFIG. 1 showing a tunnel, an air intake system, and an exhaust systemaccording to a first implementation;

FIG. 3 is a right side elevation view of the air intake system and theexhaust system of FIG. 2;

FIG. 4 is a perspective view taken from a top, rear, right side of theair intake system and the exhaust system of FIG. 3;

FIG. 5 is a perspective exploded view of the air intake system of FIG.3;

FIG. 6 is a top plan view of the tunnel of FIG. 2, with a primary airboxof the air intake system;

FIG. 7 is a front elevation view of the tunnel and the primary airbox ofFIG. 6;

FIG. 8 is a cross-sectional view of the tunnel and the primary airbox ofFIG. 6, taken along cross-section line 8-8 of FIG. 6, with a portion ofthe drive track represented;

FIG. 9 is a perspective view taken from a front, left side of thecross-section taken along cross-section line 9-9 of FIG. 6;

FIG. 10 is a right side elevation view of the exhaust system of FIG. 2;

FIG. 11 is a top plan view of the exhaust system of FIG. 10;

FIG. 12 is a schematic representation of the air intake system and theexhaust system of FIG. 3;

FIG. 13 is a cross-sectional view of the internal combustion engine ofthe snowmobile of FIG. 1;

FIG. 14 is a top plan view of a second implementation of the exhaustsystem of FIG. 10;

FIG. 15 is a rear elevation view of the exhaust system of FIG. 14;

FIG. 16 is a schematic representation of the air intake system of FIG. 3and of the exhaust system of FIG. 14;

FIG. 17 is a schematic representation of the air intake system of FIG.3, and of a third implementation of the exhaust system of FIG. 10; and

FIG. 18 is a schematic representation of the air intake system of FIG.3, and of a fourth implementation of the exhaust system of FIG. 10.

DETAILED DESCRIPTION

With reference to FIG. 1, a snowmobile 10 includes a forward end 12 anda rearward end 14. The snowmobile 10 includes a vehicle body in the formof a frame or chassis 16 which, as can be seen in FIG. 2, includes atunnel 18, an engine cradle portion 20, a front suspension module 22 andan upper structure 24.

An internal combustion engine 26 (schematically illustrated in FIG. 1)is carried in an engine compartment defined in part by the engine cradleportion 20 of the frame 16. A fuel tank 28, supported above the tunnel18, supplies fuel to the engine 26 for its operation. The engine 26receives air from an air intake system 100 (FIGS. 2 and 3) that includesa heat exchanger 130 (FIGS. 8 and 9). Air flowing into the engine 26 isfirst cooled by circulating through the heat exchanger 130 as will bedescribed in greater detail below.

An endless drive track 30 is positioned at the rear end 14 of thesnowmobile 10. The drive track 30 is disposed generally under the tunnel18, and is operatively connected to the engine 26 through a belttransmission system and a reduction drive. The endless drive track 30 isdriven to run about a rear suspension assembly 32 operatively connectedto the tunnel 18 for propulsion of the snowmobile 10. The endless drivetrack 30 has a plurality of lugs 31 extending from an outer surfacethereof to provide traction to the track 30.

The rear suspension assembly 32 includes drive sprockets 34, idlerwheels 36 and a pair of slide rails 38 in sliding contact with theendless drive track 30. The drive sprockets 34 are mounted on an axle 35and define a sprocket axis 34 a. The axle 35 is operatively connected toa crankshaft (not shown) of the engine 26. The slide rails 38 areattached to the tunnel 18 by front and rear suspension arms 40 and shockabsorbers 42. It is contemplated that the snowmobile 10 could beprovided with a different implementation of a rear suspension assembly32 than the one shown herein.

A straddle-type seat 60 is positioned atop the fuel tank 28. A fuel tankfiller opening covered by a cap 92 is disposed on the upper surface ofthe fuel tank 28 in front of the seat 60. It is contemplated that thefuel tank filler opening could be disposed elsewhere on the fuel tank28. The seat 60 is adapted to accommodate a driver of the snowmobile 10.The seat 60 could also be configured to accommodate a passenger. Afootrest 64 is positioned on each side of the snowmobile 10 below theseat 60 to accommodate the driver's feet.

At the front end 12 of the snowmobile 10, fairings 66 enclose the engine26 and the belt transmission system, thereby providing an external shellthat not only protects the engine 26 and the transmission system, butcan also make the snowmobile 10 more aesthetically pleasing. Thefairings 66 include a hood 68 and one or more side panels which can beopened to allow access to the engine 26 and the belt transmission systemwhen this is required, for example, for inspection or maintenance of theengine 26 and/or the transmission system. A windshield 69 connected tothe fairings 66 acts as a wind screen to lessen the force of the air onthe rider while the snowmobile 10 is moving.

Two skis 70 positioned at the forward end 12 of the snowmobile 10 areattached to the front suspension module 22 of the frame 16 through afront suspension assembly 72. The front suspension module 22 isconnected to the front end of the engine cradle portion 20. The frontsuspension assembly 72 includes ski legs 74, supporting arms 76 and balljoints (not shown) for operatively connecting to the respective ski leg74, supporting arms 76 and a steering column 82 (schematicallyillustrated in FIG. 1).

A steering assembly 80, including the steering column 82 and a handlebar84, is provided generally forward of the seat 60. The steering column 82is rotatably connected to the frame 16. The lower end of the steeringcolumn 82 is connected to the ski legs 74 via steering rods (not shown).The handlebar 84 is attached to the upper end of the steering column 82.The handlebar 84 is positioned in front of the seat 60. The handlebar 84is used to rotate the steering column 82, and thereby the skis 70, inorder to steer the snowmobile 10. A throttle operator 86 in the form ofa thumb-actuated throttle lever is mounted to the right side of thehandlebar 84. Other types of throttle operators, such as afinger-actuated throttle lever and a twist grip, are also contemplated.A brake actuator 88, in the form of a hand brake lever, is provided onthe left side of the handlebar 84 for braking the snowmobile 10 in aknown manner. It is contemplated that the windshield 69 could beconnected directly to the handlebar 84. Engine air inlets 27 are forwardof the handlebar 84.

At the rear end of the snowmobile 10, a snow flap 94 extends downwardfrom the rear end of the tunnel 18. The snow flap 94 protects againstdirt and snow that can be projected upward from the drive track 30 whenthe snowmobile 10 is being propelled by the moving drive track 30. It iscontemplated that the snow flap 94 could be omitted.

The snowmobile 10 includes other components such as a display cluster,and the like. As it is believed that these components would be readilyrecognized by one of ordinary skill in the art, further explanation anddescription of these components will not be provided herein.

With reference to FIGS. 6 to 9, the tunnel 18 will now be described inmore detail. The inverted U-shaped tunnel 18 has a left side portion 18a and a right side portion 18 b. The footrests 64 are connected to theleft and right side portions 18 a, 18 b. A top portion 18 c extendsbetween the left and right side portions 18 a, 18 b. The left, right andtop portions 18 a, 18 b, 18 c define a longitudinally extending space 19therebetween. The upper portion of the drive track 30 is disposed atleast partly in the space 19. The drive sprockets 34 and the axle 35 aredisposed in a forward portion of the space 19 enclosed by the forwardportion of the tunnel 18.

A passage 21 is defined in the top portion 18 c of the tunnel 18 in theform of a through hole. As can be seen in FIG. 8, the passage 21 isabove the axle 35 and is longitudinally aligned with the axle 35. Aprotrusion 21 a is defined rearwardly of the passage 21 on a bottom face18 d of the top portion 18 c. Another protrusion 21 b is definedforwardly of the passage 21 on the bottom face 18 d of the top portion18 c. In the present implementation, the protrusions 21 a, 21 b extenddownwardly from the top portion 18 c and are defined by a portion of thesheet metal of the top portion 18 c of the tunnel 18. In someimplementations, the protrusions 21 a, 21 b could be separate componentsthat are connected to the bottom face 18 d of the top portion 18 c. Theprotrusions 21 a, 21 b extend downwardly from the top portion 18 c ofthe tunnel 18 and above the drive track 30, as can be seen in FIGS. 8and 9. In some implementations, both protrusions 21 a, 21 b or only theprotrusion 21 b could be omitted.

The engine 26 is an inline, two-cylinder, two-stroke, internalcombustion engine. The two cylinders of the engine 26 are oriented withtheir cylindrical axes disposed vertically. It is contemplated that theengine 26 could be configured differently. For example, the engine 26could have more or less than two cylinders, and the cylinders could bearranged in a V-configuration instead of in-line. It is contemplatedthat in some implementations the engine 26 could be a four-strokeinternal combustion engine, a carbureted engine, or any other suitableengine capable of propelling the snowmobile 10.

Referring to FIGS. 12 and 13, the engine 26 receives air from the airintake system 100 via the engine air inlet 27 defined in the rearportion of each cylinder of the engine 26. Each air inlet 27 isconnected to a throttle body 37 of the air intake system 100. Thethrottle body 37 comprises a throttle valve 39 which rotates to regulatethe amount of air flowing through the throttle body 37 into thecorresponding cylinder of the engine 26. A throttle valve actuator (notshown) is operatively connected to the throttle valve 39 to change theposition of the throttle valve 39 and thereby adjust the opening of thethrottle valve 39 with operation of the throttle lever 86 on thehandlebar 84. It is also contemplated that the throttle valve actuatorcould be in the form of an electric motor. The electric motor couldchange the position of the throttle valve 39 based on input signalsreceived from an electronic control module (not shown) which in turnreceives inputs signals from a position sensor associated with thethrottle lever 86 on the handlebars 84. Further details regarding suchdrive-by wire throttle systems can be found in International PatentPublication No. WO 2014/005130 A1, published on Jan. 3, 2014, theentirety of which is incorporated herein by reference. The air intakesystem 100 includes a heat exchanger 130 for cooling intake air as willbe described in greater detail below.

The engine 26 receives fuel from the fuel tank 28 via injectors 41having an opening in the cylinders. The fuel-air mixture in each of theleft and right cylinders of the engine 26 is ignited by an ignitionsystem (not shown). Engine output power, torque and engine speed aredetermined in part by the ignition timing, and also by variouscharacteristics of the fuel-air mixture such as its composition,temperature, pressure and the like.

Exhaust gases resulting from the combustion events of the combustionprocess are expelled from the engine 26 via an exhaust system 200. Anexhaust outlet 29 is defined in the front portion of each cylinder ofthe engine 26. The exhaust outlets 29 are fluidly connected to anexhaust manifold 33. The exhaust system 200 includes an exhaust pipe 202which is connected to the exhaust manifold 33 and extends forwardlytherefrom to direct the exhaust gases out of the engine 26. The exhaustsystem 200 will be described in greater detail below.

A turbocharger 300 is operatively connected to the engine 26. Theturbocharger 300 has a housing 302 including an air compressor 310 andan exhaust turbine 350. The air compressor 310 includes a compressorturbine and is part of the air intake system 100. Intake air flowingpast the rotating compressor turbine is compressed thereby. The rotationof the compressor turbine is powered by the exhaust turbine 350, whichis in turn rotated by exhaust gases expelled from the engine 26 andbeing directed to flow over the blades of the exhaust turbine 350. It iscontemplated that, in some implementations, the air compressor 310 couldbe a supercharger, in which the compressor turbine would be directlypowered by the engine 26.

With reference to FIGS. 2 to 9, the air intake system 100 will bedescribed. Air from the atmosphere flows through side apertures 113defined in an upper portion 25 of the upper structure 24 of the chassis16. Screens 114 connected to the upper portion 25 may assist inpreventing debris, dust particles, snow and/or water to enter the sideapertures 113. The air then flows through a secondary airbox 110 throughan inlet 112 defined in the front portion of the snowmobile 10. Theinlet 112 is defined in the upper portion 25 of the upper structure 24.Screens and/or filters may be connected to the inlet 112 of thesecondary airbox 110. The secondary airbox 110 is disposed above thefront suspension module 22. An outlet 116 is defined in the middleportion on the right side of the secondary airbox 110. The outlet 116 isfluidly connected to an inlet 312 of the air compressor 310 disposed onthe right side of the engine 26. It is contemplated that the secondaryairbox 110 could be omitted and that air from the atmosphere coulddirectly enter into the inlet 312 without going through the secondaryairbox 110.

When the air from the atmosphere is compressed by the air compressor310, the air warms up because of the friction between the air moleculesand because of the increase of pressure. In addition, when the exhaustgas flows through the exhaust turbine 350, some of the heat of theexhaust gas heats up the housing 302, which in turn transfers some ofthat heat to the air being compressed in the air compressor 310, warmingup the compressed air even more. The compressed air then flows out ofthe air compressor 310 through an outlet 314, into a conduit 316 andinto a primary air box 120. The secondary airbox 110 defines a firstchamber of the air intake system 100, and the primary airbox 120 definesa second chamber of the air intake system 100. In some implementations,the chambers defined by the secondary airbox 110 and the primary airbox120 act as resonators lowering the noise exiting through the air intakesystem 100.

As best seen in FIGS. 6 and 7, the primary air box 120 is connected to aforward portion of the tunnel 18 on the top portion 18 c thereof. Theprimary air box 120 is fastened to the tunnel 18, but it is contemplatedthat it could be connected thereto otherwise. It is also contemplatedthat the primary air box 120 could be connected to another portion ofthe snowmobile 10, instead of the tunnel 18. The primary air box 120 isa heat exchanger 130 (FIGS. 8 and 9). The heat exchanger 130 has a heatexchanger engine air inlet 132 fluidly connected to the conduit 316, twoheat exchanger engine air outlets 134 fluidly connected to each engineair inlet 27, two cooling air inlets 136 for receiving air from theatmosphere, and a cooling air outlet 138 fluidly connected between thecooling air inlet 136 and the passage 21 defined in the tunnel 18. Asbest seen in FIGS. 6 to 9, the cooling air inlets 136 and the coolingair outlet 138 are disposed laterally between the left and right sideportions 18 a, 18 b of the tunnel 18. In addition, the cooling airinlets 136 and the cooling air outlet 138 are disposed vertically higherthan the top portion 18 c of the tunnel 18. It is contemplated that thecooling air inlets 136 and the cooling air outlet 138 could bepositioned otherwise.

Referring to FIGS. 8 and 9, the heat exchanger 130 includes anintercooler 140. The intercooler 140 is made of extruded metal, but itis contemplated that it could be made otherwise. The intercooler 140defines paths 144 (FIG. 8), 146 (FIG. 9) separate from each other, eachone being schematically represented by an arrow. The path 144 includes aplurality of channels 144 a fluidly connecting the heat exchanger engineair inlet 132 to the heat exchanger engine air outlets 134, each onebeing schematically represented by an arrow. The channels 144 a extendgenerally longitudinally with respect to the primary air box 120. Theprimary air box 120 further includes a baffle 150 extending above theintercooler 140 for separating the paths 144, 146. The baffle 150directs the air entering the primary air box 120 through the heatexchanger engine air inlet 132 toward a rear wall 122 thereof. Since thepaths 144, 146 are separate from each other, the air flowing from theheat exchanger engine air inlet 132 to the heat exchanger engine airoutlets 134, and the air flowing from the cooling air inlets 136 to thecooling air outlet 138 do not mix. In some implementations, it iscontemplated that the two paths 144, 146 could be in fluid communicationand could allow for the air flowing through the intercooler 140 to mixat least partially.

The path 146 includes a plurality of channels 146 a (FIG. 9) fluidlyconnecting the cooling air inlets 136 to the cooling air outlet 138,each one being schematically represented by an arrow. The channels 146 aextend generally vertically and parallel to the rear wall 122 of theprimary airbox 120. As such, the path 144 is perpendicular to the path146. The paths 144, 146 are in thermal communication, which means thatwhen the compressed air flows through the path 144, some of its heat istransferred to the air flowing through the path 146 via the heatexchanger 130. The air flowing through the cooling air inlets 136 andthrough the path 146 is air from the atmosphere and is cooler than thecompressed air flowing through the path 144. It is contemplated that theair flowing through the path 146 could be, in some implementations, airfrom the atmosphere contained within the body of the snowmobile 10 orthe engine compartment thereof. As such, the compressed air flowing fromthe heat exchanger engine air inlet 132 to the heat exchanger engine airoutlets 134 is cooled by the air flowing from the cooling air inlets 136to the cooling air outlet 138. In other words, as air from theatmosphere flows along the path 146, it is heated up by the heatexchanger 130 that assists in transferring some of the heat from thecompressed air flowing through the path 144 to the air from theatmosphere flowing through the path 146. As a result, the compressed airflowing through the heat exchanger engine air outlets 134 is cooler thanthe compressed air flowing through the heat exchanger engine air inlet132, and provides for a denser intake charge for the engine 26.

As will be described with reference with FIGS. 8 and 9, the passage 21defined in the top portion 18 c of the tunnel 18 further assists incooling the compressed air flowing through the passage 144. When thesnowmobile 10 is being propelled, the drive track 30 is rotating insidethe space 19 of the tunnel 18. Rotation of the drive track 30, and ofthe lugs 31 extending therefrom, creates a low pressure zone 160 nearthe passage 21. The low pressure zone 160 is understood to be a zonenear the passage 21 having a pressure that is lower than the atmosphericpressure. The decrease of atmospheric pressure within the low pressurezone 160 is caused by the rotation of the drive track 30 when thesnowmobile 10 is propelled forwardly. As such, when the drive track 30propels the snowmobile 10 forwards, the lugs 31 have an effect similarto that of the blades of a fan, in that the lugs 31 move the air near orwithin the passage 21 forwardly therefrom, and thus locally decreasingthe air pressure. In addition, the protrusion 21 a has a venturi-likeeffect and breaks the boundary layer of the air flowing between bottomface 18 d of the tunnel 18 and the drive track 30 and causes turbulentflow of the air forward of the protrusion 21 a and within the passage21. As a result, the low pressure zone 160 is forward of the protrusion21 a and at least partially rearward of the protrusion 21 b.

When the low pressure zone 160 is formed, air from the atmosphere isinduced to flow into the heat exchanger 130 through the cooling airinlets 136, through the intercooler 140 through the path 146, throughthe cooling air outlet 138 and into the passage 21. As such, theefficiency of the heat exchanger 130 is increased when the snowmobile 10is being propelled since more heat can be transferred from the airflowing through the path 144 to the air flowing through the path 146 asair from the atmosphere is induced to flow through the path 146.

Referring to FIG. 12, other components of the air intake system 100 willbe described. A blow-off conduit 170 having a blow-off valve 172 isfluidly connected between the secondary airbox 120 and the primaryairbox 130. The blow-off valve 172 is open under certain circumstances,such as when the compressed air exiting the outlet 314 has a pressurethat is above a predetermined pressure threshold. For example, insituations where the air compressor 310 is operated and the throttlevalve 39 is closed, the air compressor 310 has to spool down and theblow-off valve 172 opens to release the excess pressure. The air intakesystem 100 further includes a bypass conduit 180 (FIG. 12) fluidlyconnecting the secondary airbox 110 to the primary airbox 120. Thebypass conduit 180 is thus fluidly connected between the engine airinlets 27 and the secondary airbox 120, which is positioned upstream ofthe air compressor 350. Air flowing through the bypass conduit 180 flowsthrough the path 144, i.e. the air flows through the heat exchangerengine air inlet 132, is cooled by the intercooler 140, flows throughthe heat exchanger engine air outlets 134, and flows to the engine airinlets 27. As such, the bypass conduit 180 allows air from theatmosphere to bypass the air compressor 310 when the snowmobile 10 isridden on a terrain having an altitude near sea level and/or undercertain circumstances which will be described in more detail below. Abypass valve 182 selectively controls a flow of air flowing through thebypass conduit 180. The bypass valve 182 is open when the turbocharger300 is not operating. It is contemplated that the bypass valve 182 couldalso open when the engine 26 is operated below a threshold operatingcondition that could be, for example, a threshold engine speed, or whenthe engine 26 is operated at idle.

Referring to FIGS. 10 to 12, a first implementation 200 a of the exhaustsystem 200 will be described. The exhaust gas expelled from the engine26 flows through the exhaust outlets 29 and into the exhaust pipe 202.As best seen in FIG. 11, the exhaust pipe 202 is curved and has avarying diameter along its length and is typically referred to as atuned pipe. Other types of exhaust pipes 202 are contemplated. The pipe202 includes a pipe inlet 203 fluidly connected to the exhaust manifold33, a pipe outlet 204 located in a middle portion of the pipe 202, and apipe outlet 206 located at the end of the pipe 202. The pipe 202 furtherhas a divergent portion 205 a adjacent to the pipe inlet 203, and aconvergent portion 205 b adjacent the pipe outlet 206. The pipe outlet204 is positioned upstream from the convergent portion 205 b. The pipeoutlet 206 is positioned downstream from the convergent portion 205 b.

The exhaust turbine 350 is connected to the exhaust system 200 a foroperating the air compressor 310. The exhaust turbine 350 includes anexhaust gas inlet 352 fluidly connected to the pipe outlet 206 forreceiving the exhaust gas from the exhaust pipe 202. The exhaust turbine350 further includes an exhaust gas outlet 354 connected to a muffler400. The exhaust gas then flows through the muffler 400 into theatmosphere via a muffler outlet 420. As best seen in FIGS. 10 and 12,the muffler 400 has a muffler inlet 402, a muffler inlet 404, anexpansion chamber 406 and an expansion chamber 408. A series of conduits410 extend between the expansion chambers 406, 408. For clarity, onlyone of the conduits 410 fluidly connects the expansion chambers 406,408, but it is contemplated that a plurality of conduits 410 couldfluidly connect the expansion chambers 406, 408. In someimplementations, there could be more than the two expansion chambers406, 408 in the muffler 400 and the conduits 410 could fluidly connectthem. The conduits 410 extend in expansion chambers 412 defined betweenthe chambers 406, 408. The conduits 410 have through holes definedtherein, and the expansion chambers 412 include sound-absorbingmaterials to further muffle the acoustic wave caused by the flow of theexhaust gas schematically shown by arrows in FIG. 12. In someimplementations, the expansion chambers 406, 408 could include a seriesof baffles in order to further muffle the acoustic wave caused by theflow of the exhaust gas flowing through the muffler 400. The mufflerinlet 402 is defined in the expansion chamber 406 at the end of one ofthe conduits 410 that is fluidly connected to the primary exhaustconduit 210. The muffler inlet 404 is defined in the expansion chamber408 and is fluidly connected to the secondary exhaust conduit 214. Themuffler outlet 420 is defined on the bottom of the muffler 400 at theend of one of the conduits 410.

Still referring to FIGS. 10 to 12, a primary exhaust conduit 210 fluidlyconnects the pipe outlet 204 to the muffler inlet 402, and defines atleast a portion of an exhaust flow path 220. The exhaust flow path 220extends from the pipe outlet 204 to the muffler inlet 402. A primaryvalve 222 is disposed in the primary exhaust conduit 210. The primaryvalve 222 selectively controls the flow of exhaust gas flowing throughthe exhaust flow path 220. When the primary valve 222 is open, theexhaust gas flowing through the exhaust flow path 220 flows in theprimary exhaust conduit 210, through one of the conduits 410, throughthe muffler inlet 402 into the expansion chamber 406, then into theexpansion chamber 408 through the conduits 410, then through the muffleroutlet 420 and to the atmosphere, as schematically shown by the arrowsin FIG. 12. When the exhaust gas flows through the exhaust flow path220, the muffler 400 reduces the noise emitted by the engine 26 and/orthe exhaust gas flowing to the atmosphere since the exhaust gas flowsthrough the expansion chamber 406, the conduits 410 and the chambers412, and the expansion chamber 408 before flowing to the atmosphere.

A secondary exhaust conduit 214 fluidly connects the exhaust gas outlet354 of the exhaust turbine 350 to the muffler inlet 404, and defines atleast a portion of an exhaust flow path 230. The exhaust flow path 230extends from the pipe outlet 206 to the muffler inlet 404. The exhaustturbine 350 is thus fluidly connected along the exhaust flow path 230between the pipe outlet 206 and the muffler inlet 404. A secondary valve232 is disposed in the secondary exhaust conduit 214 (FIG. 12). Thesecondary valve 232 selectively controls the flow of exhaust gas flowingthrough the exhaust flow path 230.

Referring to FIG. 12, when the secondary valve 232 is open, the exhaustflow path 230 defines a more direct flow path from the exhaust pipe 202than the exhaust flow path 220 since the exhaust gas avoids flowingthrough the expansion chamber 406 and the plurality of conduits 410.Instead, the exhaust gas flows through the muffler inlet 404 into theexpansion chamber 408, and then through one of the conduits 410 and onto the atmosphere through the muffler outlet 420. In this respect and ascan be seen in FIGS. 10 and 12, the secondary exhaust conduit 214 andthe muffler outlet 420 are nearly coaxial with one another, whichfacilitates the flow of the exhaust gas from the exhaust flow path 230to the atmosphere. Allowing the exhaust gas to flow through the exhaustflow path 230 may assist in reducing an amount of backpressure appearingin the exhaust system 200 a compared to a situation where the exhaustgas flows through the exhaust flow path 220. Backpressure is understoodto be the resistance to the flow of the exhaust gas between the engine26 and the muffler outlet 420 due, at least in part, to twists, bends,obstacles, turns and right angles present in the various components ofthe exhaust system 200. In present technology, reducing backpressure canassist in optimizing performance of the engine 26, as high backpressurecan negatively impact the efficiency of the engine performance Reducingthe amount of backpressure in the exhaust system 200 a may also have theeffect of reducing what is known as “turbo lag”, which is a delay in theresponse of a turbocharged engine after the throttle lever 86 has beenmoved for operating the throttle system.

Furthermore, under certain conditions, when the exhaust gas flowsthrough the exhaust flow path 230, the muffler 400 reduces the noiseemitted by the engine 26 and/or the exhaust gas flowing to theatmosphere, but to a lesser extent than when the exhaust gas flowsthrough the exhaust flow path 220 since the exhaust gas flows onlythrough the expansion chamber 408 and one of the chambers 412 beforeflowing to the atmosphere.

An illustrative scenario of the operation of the snowmobile 10 havingthe air intake system 100 and the exhaust system 200 a is describedbelow with reference to FIG. 12. It is to be noted that the componentsschematically shown in FIG. 12 are not to scale and could be configuredotherwise than what is presented herein. The following scenario, and thefurther description of different implementations of the exhaust system200, describe how the flow of exhaust gas from the engine 26 can becontrolled using the exhaust system 200.

Referring to FIG. 12, air from the atmosphere enters the secondaryairbox 110 through the inlet 112 as described above. When theatmospheric pressure is above a threshold atmospheric pressure, such as1 Bar, which could be the case when the snowmobile 10 is ridden on aterrain nearly at sea level for example, the bypass valve 182 is open.Thus, the air from the atmosphere flows from the secondary airbox 110 tothe primary airbox 120 through the bypass conduit 180, and thus bypassesthe air compressor 310. The air flows through the primary airbox 120,through the path 144 defined in the intercooler 140, through the heatexchanger engine air outlets 134 and on to the engine air inlets 27.Combustion events occur in the engine 26 and the exhaust gas resultingfrom the combustion events is expelled through the engine exhaustoutlets 29 in the exhaust pipe 202.

In this scenario, the bypass valve 182 and the primary valve 222 areopen, and the secondary valve 232 is closed. The exhaust gas flowsthrough the exhaust flow path 220 to the expansion chamber 406, theconduits 410 and chambers 412, the expansion chamber 408, the muffleroutlet 420 and to the atmosphere. Since the secondary valve 232 isclosed, the exhaust turbine 350 is prevented from spooling as theexhaust gas cannot flow through the exhaust flow path 230. The aircompressor 310 is also prevented from spooling and the engine 62 is thusoperated as a naturally aspirated engine. As such, when the primaryvalve 222 is open and the secondary valve 232 is closed, the exhaust gasflows sequentially from the engine 26 to the exhaust pipe 202, throughthe exhaust flow path 220, the expansion chambers 406, 408 of themuffler 400 and on to the atmosphere.

When the atmospheric pressure is below the threshold atmosphericpressure, such as when the snowmobile 10 is ridden on terrains having ahigh altitude for example, the bypass valve 182 is closed, the primaryvalve 222 is closed and the secondary valve 232 is open. Air from theatmosphere enters the secondary airbox 110 through the inlet 112, flowsthrough the outlet 116 and enters the air compressor 310 through theinlet 312. The air is compressed by the air compressor 310 and is heatedup because of the compression. The compressed air then flows through theoutlet 314 into the conduit 316 and through the heat exchanger engineair inlet 132. The compressed air flows in the heat exchanger 130through the path 144 and is cooled by the air flowing through the path146 in the intercooler 140. The cooled compressed air flows through theheat exchanger engine air outlets 134 and on to the engine air inlets27. Combustion events occur in the engine 26 and the exhaust gasresulting from the combustion events are expelled through the engineexhaust outlets 29 in the exhaust pipe 202. The exhaust gas flowsthrough the pipe outlet 206, and through the exhaust flow path 230.Thus, the exhaust gas flows through the exhaust turbine inlet 352 andmakes the exhaust turbine 350 spool. The housing 302 of the turbocharger300 is heated up as the exhaust gas flows past the exhaust turbine 350,as described above. The exhaust gas flows through the exhaust turbineoutlet 354 into the secondary exhaust conduit 214 and along the exhaustflow path 230. The exhaust gas flows through the exhaust flow path 230until the muffler inlet 404, enters the expansion chamber 408 and isexpelled to the atmosphere through the muffler outlet 420. As such, whenthe primary valve 222 is closed and when the secondary valve 232 isopen, the exhaust gas flows sequentially from the engine 26 to theexhaust pipe 202, through the exhaust flow path 230 including theexhaust turbine 350, through the expansion chamber 408 and one of theexpansion chambers 412 of the muffler 400 and on to the atmosphere.

It is contemplated that when the secondary valve 232 is open, theprimary valve 222 could be selectively open in order to allow a portionof the exhaust gas flowing through the exhaust pipe 202 to flow throughthe exhaust flow path 220. Such controlled opening of the primary valve222 could regulate the operation of the turbocharger 300, and thusregulate the amount of compressed air sent to the engine 26. In someimplementations, opening the primary valve 222 could aid in decreasingbackpressure when the turbocharger 300 is not spooling. Under certainconditions, the blow-off valve 172 and/or the bypass valve 182 could beopen as well.

The primary and secondary valves 222, 232 are selectively movablebetween open and closed positions depending on a threshold engineoperating condition and/or a threshold atmospheric pressure. Withreference to FIG. 12, the selective controlling of the primary andsecondary valves 222, 232 is operated by a system controller 500operatively connected to an engine control unit (or E.C.U.) 502 and/orthe electrical system (not shown) of the snowmobile 10. The enginecontrol unit 502 is operatively connected to the engine 26. The systemcontroller 500 is operatively connected to an atmospheric pressuresensor 504. The primary valve 222 is moved between the open and closedpositions by a motor 522 operatively connected to the system controller500. The secondary valve 232 is moved between the open and closedpositions by a motor 532 operatively connected to the system controller500. The bypass valve 182 is operatively connected to a motor 582 formoving the bypass valve 182, and the motor 582 is operatively connectedto the system controller 500. When the atmospheric pressure sensor 504detects that the atmospheric pressure threshold is reached, theatmospheric pressure sensor 504 sends an electronic signal to the systemcontroller 500. The system controller 500 then executes a program storedin memory to control the motor 522 and/or the motor 532 for selectivelycontrolling the primary and secondary valves 222, 232. The programexecuted by the system controller 500 may be based on control mapsand/or algorithms stored in the memory. Other configurations of thesystem controller 500, engine control unit 502, atmospheric pressuresensor 504 and motors 522, 532 are contemplated.

It is contemplated that in a situation where the throttle lever 86 ismoved such that a high power request is made to the engine 26, forexample during acceleration of the snowmobile 10, the primary valve 222could be closed and the secondary valve 232 could be open for causingthe turbocharger 300 to spool up and feed compressed air to the engine26. The engine 26 would then benefit from a denser intake charge andwould have increased power output compared to a similar engine thatwould be naturally aspirated. Then, if the throttle lever 86 were to bereleased, the primary valve 222 could be opened in order to reduce theamount of exhaust gas flowing through the exhaust flow path 230 in orderfor the turbocharger 300 to spool down more rapidly, since the exhaustturbine 350 and the air compressor 310 are spooling but are no longerrequired. Reducing the amount of exhaust gas flowing through the exhaustflow path 230 while the turbocharger 350 is spooling down could reducethe amount of backpressure in the exhaust system 200 a.

It is contemplated that the threshold atmospheric pressure may be apredetermined range of atmospheric pressure. In such an implementation,the primary and secondary valves 222, 232 are configured to remain intheir current positions when the atmospheric pressure passes the mark ofthe upper and lower limits of the predetermined range of atmosphericpressure. For example, in implementations where the predetermined rangeof atmospheric pressure is between 800 and 1000 mBar, the exhaust system200 a is configured to close the secondary valve 232 when theatmospheric pressure is above 1000 mBar, thus preventing operation ofthe turbocharger 300. When the atmospheric pressure is between 800 and1000 mBar, the secondary valve 232 remains in its current closedposition. The exhaust system 200 a is configured to open the secondaryvalve 232 when the atmospheric pressure is below 800 mBar, thuspermitting operation of the turbocharger 300. It is contemplated that insome implementations the secondary valve 232 could be open when theatmospheric pressure is between 800 and 1000 mBar and the engine 26 isoperated above the threshold operating condition of the engine 26. Thethreshold operating condition of the engine 26 could be, for example, athreshold engine speed.

An exemplary scenario regarding these aspects is provided for betterunderstanding. Initially, when the snowmobile 10 is ridden at a firstaltitude where the atmospheric pressure is 1040 mBar, the secondaryvalve 232 is closed. Then, when the snowmobile is ridden at a secondaltitude where the atmospheric pressure decreases to 950 mBar, such aswhen climbing a mountain, the secondary valve 232 remains in its currentclosed position. When the snowmobile is ridden at a third altitude wherethe atmospheric pressure drops to 790 mBar, the secondary valve 232opens when the atmospheric pressure passes the 800 mBar mark. In thissituation, the snowmobile 10 benefits from the engine 26 receiving adenser intake charge because of the operation of the turbocharger 300,thus increasing the power output of the engine 26 compared to a similarengine that would be naturally aspirated.

When the snowmobile 10 is ridden from the third altitude to the secondaltitude, the atmospheric pressure may increase from 790 mBar to 950mBar. The secondary valve 232 remains in its current open position whenthe atmospheric pressure passes the 800 mBar mark. When the snowmobile10 is ridden from the second altitude to the first altitude, theatmospheric pressure increases from 950 mBar to 1040 mBar. The secondaryvalve 232 is closed when the atmospheric pressure passes the 1000 mBarmark.

Having the secondary valve 232 opening and closing in accordance withthe above example may assist in preventing the secondary valve 232 toopen and close repeatedly when the atmospheric pressure is near thethreshold atmospheric pressure.

Referring to FIGS. 14 to 16, a second implementation 200 b of theexhaust system 200 will be described. Various components described inrelation to the first implementation of the exhaust system 200 a arefound in the exhaust system 200 b, have the same functions and will notbe described in detail, unless mentioned otherwise.

In the exhaust system 200 b, the turbocharger 300 has a housing 302 bthat differs from the housing 302 shown in FIG. 11 in that the housing302 b defines the pipe outlet 204 and includes the primary valve 222.The primary pipe conduit 210 is fluidly connected between the pipeoutlet 204 and the muffler inlet 402, and defines at least a portion ofthe exhaust flow path 220. As can be seen in FIGS. 11 and 14, theexhaust system 200 b is a more compact package compared to the exhaustsystem 200 a. The operation and the flow characteristics of the exhaustsystem 200 b are similar to the ones of the exhaust system 200 a. Thus,the primary and secondary valves 222, 232 are operated as describedabove with respect to the exhaust system 200 a. As such, the valves 222,232 can be selectively closed or open depending on the atmosphericpressure and/or a threshold engine speed for controlling the flow ofexhaust gas along the exhaust flow paths 220, 230.

Referring to FIG. 17, a third implementation 200 c of the exhaust system200 will be described. Various components described in relation to thesecond implementation of the exhaust system 200 b are found in theexhaust system 200 c, have the same functions and will not be describedin detail, unless mentioned otherwise.

The exhaust system 200 c has a transfer conduit 240 (also referred to asa “bridge pipe”) fluidly connecting the primary and secondary exhaustconduits 210, 214. The transfer conduit 240 is positioned downstreamfrom the primary valve 222 and upstream from the secondary valve 232. Insituations where the turbocharger 300 is not required but is spoolingdown, such as when the throttle lever 86 has just been released asdescribed above, the secondary valve 232 is open and the primary valve222 could, under certain circumstances, be opened. When the primaryvalve 222 is open, a portion of the exhaust gas flowing through theexhaust flow path 220 flows through an exhaust flow path 250 defined atleast partially by the transfer conduit 240 and the secondary exhaustconduit 214. The exhaust gas flowing through the exhaust flow path 250flows through the transfer conduit 240, the secondary exhaust conduit214, the muffler inlet 404, the expansion chamber 408, one of theconduits 410 and on to the atmosphere through the muffler outlet 420.The exhaust flow path 250 is more direct than the exhaust flow path 220as it bypasses the expansion chamber 406 and at least some of theconduits 410 of the muffler 400. The exhaust flow path 250 also bypassesthe exhaust turbine 350 and may assist in reducing the amount ofbackpressure in the exhaust system 200 c. As such, by selectively movingthe primary and secondary valves 222, 232, the exhaust gas can flow fromthe exhaust flow path 220 to the exhaust flow path 230.

It is contemplated that, under certain circumstances, the primary valve222 could be closed, the secondary valve 232 could be closed and theturbocharger 300 could be operated. In such situations, the exhaust gasexiting the exhaust turbine 350 and flowing through the secondaryexhaust conduit 214 could flow through the transfer conduit 240, and inthe muffler 400 through the muffler inlet 402. The exhaust gas couldthen flow through the expansion chamber 406, the conduits 410 and thechambers 412, the expansion chamber 408 and on to the atmosphere. Assuch, by selectively moving the primary and secondary valves 222, 232,the exhaust gas can flow from the exhaust flow path 230 to the exhaustflow path 220. The muffler 400 could reduce the noise emitted by theengine 26 and/or the exhaust gas flowing to the atmosphere to a greaterextent than when the exhaust gas flows through the exhaust flow path 230when the turbocharger 300 is in operation. However, it is contemplatedthat such configuration of the exhaust system 200 c could increase anamount of backpressure therein compared to the above example.

Referring to FIG. 18, a fourth implementation 200 d of the exhaustsystem 200 will be described. Various components described in relationto the second implementation of the exhaust system 200 b are found inthe exhaust system 200 d, have the same functions and will not bedescribed in detail, unless mentioned otherwise.

The exhaust flow path 220 extends from the exhaust flow path 230. Theprimary and secondary valves 222, 232 are omitted and a valve 260 ispositioned at the fluid junction of the exhaust flow paths 220, 230. Thevalve 260 is an inverted valve that is movable for simultaneouslycontrolling the flow of exhaust gas flowing through the exhaust flowpaths 220, 230. A motor 560 is operatively connected to the invertedvalve 260 and to the system controller 500 for selectively moving theinverted valve 260. The inverted valve 260 is movable between a firstposition for causing the exhaust gas to flow through the exhaust flowpath 220, and a second position for causing the exhaust gas to flowthrough the exhaust flow path 230. The inverted valve 260 can also bemoved into a plurality of intermediate positions between the first andsecond positions for selectively controlling the flow of the exhaust gasflowing simultaneously through the exhaust flow paths 220, 230. Thus,when the inverted valve 260 is in one of the intermediate positions, aportion of the exhaust gas flows through the exhaust flow path 220, andthe remainder portion of the exhaust gas flows through the exhaust flowpath 230. In such circumstances, the inverted valve 260 can regulate theoperation of the turbocharger 300 and thus regulate the amount ofcompressed air sent to the engine 26 while simultaneously controllingthe flow of the exhaust gas through the exhaust flow paths 220, 230. Theinverted valve 260 cannot be moved to a position preventing the flow ofthe exhaust through both the exhaust flow paths 220, 230 simultaneously.

Under certain circumstances, the exhaust system 200 d is simpler tooperate than the exhaust systems 200 a, 200 b, 200 c including theprimary and secondary valves 222, 232 since only the inverted valve 260has to be moved for selectively controlling the flow of exhaust gasthrough the exhaust flow path 220 and/or the exhaust flow path 230.

Modifications and improvements to the above-described implementations ofthe present technology may become apparent to those skilled in the art.The foregoing description is intended to be exemplary rather thanlimiting. The scope of the present technology is therefore intended tobe limited solely by the scope of the appended claims.

What is claimed is:
 1. A snowmobile comprising: a frame including atunnel, the tunnel having a passage defined therethrough; at least oneski connected to the frame; an engine supported by the frame and havingan engine air inlet; a rear suspension assembly operatively connected tothe tunnel; and a drive track supported by the rear suspension assemblyand disposed at least in part below the tunnel, the drive track beingoperatively connected to the engine; and a heat exchanger connected tothe tunnel, the heat exchanger comprising: a heat exchanger engine airinlet fluidly connected to atmosphere; a heat exchanger engine airoutlet fluidly connected between the heat exchanger engine air inlet andthe engine air inlet; a cooling air inlet fluidly connected to theatmosphere; and a cooling air outlet fluidly connected between thecooling air inlet and the passage of the tunnel.
 2. The snowmobile ofclaim 1, wherein an air from the heat exchanger engine air inlet to theheat exchanger engine air outlet is cooled by an air from the coolingair inlet to the cooling air outlet.
 3. The snowmobile of claim 1,wherein the an air inside the heat exchanger from the heat exchangerengine air inlet to the heat exchanger engine air outlet is fluidlyseparate from an air inside the heat exchanger from the cooling airinlet to the cooling air outlet.
 4. The snowmobile of claim 1, furthercomprising an intercooler disposed inside the heat exchanger, theintercooler defining a first path for air flowing from the cooling airinlet to the cooling air outlet, and the intercooler defining a secondpath for air flowing from the heat exchanger engine air inlet to theheat exchanger engine air outlet, the first path being fluidly separatefrom the second path, and the first path being in thermal communicationwith the second path.
 5. The snowmobile of claim 4, wherein the firstpath is perpendicular to the second path.
 6. The snowmobile of claim 1,wherein: the tunnel comprises a left side portion and a right sideportion; and the cooling air inlet and the cooling air outlet aredisposed laterally between the left and right side portions.
 7. Thesnowmobile of claim 6, wherein: the tunnel further comprises a topportion connected between the left and right side portions; and thecooling air inlet and the cooling air outlet are disposed verticallyhigher than the top portion.
 8. The snowmobile of claim 7, wherein, whenthe snowmobile is being propelled, rotation of the drive track creates alow pressure zone near the passage, the low pressure zone inducing airto flow into the heat exchanger through the cooling air inlet, exit theheat exchanger through the cooling air outlet and to flow through thepassage.
 9. The snowmobile of claim 8, wherein: the passage is definedin the top portion; a protrusion is defined rearwardly of the passage ona bottom face of the top portion; and the low pressure zone is forwardof the protrusion.
 10. The snowmobile of claim 1, wherein the heatexchanger is connected to a forward portion of the tunnel.
 11. Thesnowmobile of claim 1, wherein the snowmobile further comprises a frontaxle operatively connected between the engine and the drive track, thepassage being above the front axle and being longitudinally aligned withthe front axle.
 12. The snowmobile of claim 1, wherein the snowmobilefurther comprises an air compressor fluidly connected between anatmosphere and the heat exchanger engine air inlet to deliver compressedair to the engine via the heat exchanger.
 13. The snowmobile of claim12, wherein: the air compressor is part of a turbocharger; the enginecomprises an engine exhaust outlet fluidly connected to theturbocharger; and a flow of exhaust gas flows out of the engine throughthe engine exhaust outlet for operating the turbocharger, and then tothe atmosphere via the turbocharger.